(1PW \ \ ?

5 d N P A 9 5 2%" PARTICLE BEAM FUSION

J If7 Sandia laboratories -I

1 t k

driver development -+ electrons- I I

SANDIA E B F A I I E B F A I I

applications driver

LLL I LASL SHIVA I NOVA Antares

pulsed

technology development

cost/joule, $

energy efficiency

fusion power

8 7 1000 300 300

25% 25% .06% .2% 1.8%

leading ICF drivers

1984 i operational date

an overall efficiency of 30 percent, a driver cost of $40 per joule, and a pellet fabrication cost of $0.10, power can be generated at costs which are competitive with other advanced energy sources. Less stringent technical requirements (pellet gain of 5-10) would be adequate for hybrid applications to supplement a light water reactor economy. Such a relatively low gain pellet would be simpler to fab- ricate, would rely on less complex physics issues, and would thus lower the overall risk at an early stage in the evolution of our know-

1977 1983

EBFA I

EBFA I1

REP

4-

-4-

beams and focused laser beams must include many other factors such as beam transport, and target coupling, as well as target design and fabrication. These issues are being investigated to determine if the perceived practical benefits of particle beam fusion can indeed be realized. The practical considera- tions are exemplified in a com- parison of the leading ICF drivers. The plan being followed by Sandia involves using the Electron Beam Fu- sion Accelerator (EBFA) to meet three objectives by 1985: significant burn using EBFA I , net energy gain based on an upgrade of EBFA to

the 2 megajoule (MJ) level (EBFA II), and demonstration of a single module of EBFA II operated in the repetitive pulse mode. These goals are dependent, of course, on suc- cess in solving several key techni- cal problems under investigation. If these technical problems can be solved, then practical applications to fusion power could be consi- dered. The potential for these ap- plications has been studied using economic models that allow one to derive the cost of power based on various assumptions. For instance, our economic analyses have shown that with a pellet gain of 50 to 100,

peak power TW i 30 1 60 I I 250 I pellet energy, kJ I 1000 I 2000 I 15 1 250 I 100

pulse width, ns 1 4 0 / 4 0 1 . 1 I l I 1

ledge.

.

DISCLAIMER

Portions of this document may be illegible electronic image products. Images are produced from the best available original document.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi- bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom- mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

. .

Introduction Sandia’s Particle Beam Fusion Program is investigating several driver options, based on pulsed power technology, with the goal of demonstrating a practical ignitor for Inertial Confinement Fusion (ICF) Reactors. The interrelated aspects of power conditioning and com- pression, beam-target interaction, and target ignition are being studied. The issues of efficiency, reliability and multiple pulse capa- bility are being integrated into the program to provide a viable ap- proach to an experimental power reactor. On a shorter time scale we expect to derive important military- related benefits from attendant re- search and facility development. The Sandia pulsed power activity

began in the mid-1960s in support of the program to demonstrate the hardness of weapon systems com- ponents to nuclear weapons ef- fects. A similar and complementary effort in weapons effects simulation has also been carried out by the Department of Defense. The appli- cation of this technology has broadened over the years to in- clude development of ultra-high power electron and ion beam ac- ‘celerators, techniques for plasma heating, and laser excitation. The two most important advan- tages of pulsed power driven fusion are the inherent low cost and high efficiency of high current particle accelerators. However, comparison of the relative merits of particle

chamber radius as a function

of pellet yield

.

1. radius in meters 2. 3. 4.

30 I I

.-

With either a pure fusion or a hy- brid approach, it is necessary to have sufficient "standoff" between the injector and the explosion for reliable long life operation of reac- tor components. Significant ad- vances have been made in energy transport using plasma channels to guide a focused particle beam to the target. Here we see a plasma channel formed by a pulsed 10

psec discharge in air. In this exper- iment the discharge is initiated and thus directed by a fine wire; in a reactor, a laser or other means will be needed to initiate the discharge on a repetitive basis. Contrary to the laser reactor ap- proaches which cannot use a dense buffer gas in the reaction chamber, we are not faced with the typical problems of first wall erosion due to

x-rays and debris. On the other hand, these explosion by-products (- 20% of the pellet yield) are stopped by the buffer gas and their energy is con- verted into a "fireball" near the pellet, which expands and applies an over pressure to the first wall. Fortunately, this overpressure decays rapidly with radius so that reasonably sized chambers can accommodate this loading.

Self Magnetically Insulated Transmission Lines (MITL)

Although we are considering sys- tems tradeoffs and technology re- quirements for reactors, our immediate problem is to de- monstrate feasibility of target igni- tion. This entails several physics

self magnetically insulated

transmission lines

questions which have yet to be answered. The matter of reliably delivering an energy of 1 MJ and a power level of - l O I 4 watts (W) to the target has been of primary con- cern because of the electrical breakdown of materials. This prob- lem has been largely circumvented by use of magnetically insulated transmission lines and by beam transport in plasma channels. (The development of the MITL concept has involved contributions from the

Kurchatov Institute, Physics Inter- national as well as Sandia Labs.) The concept of using the self- magnetic field of a powerful elec- tromagnetic pulse to inhibit breakdown is central to our ap- proach of power concentration. Without this self-field approach, the power which could be transmitted in a reasonably sized transmission line would be less than .1 terawatt (Tw). On the other hand, at high power levels the self-magnetic field

time dependent- 2-D simulation

of magnetically insulated coax

1.5

1

.5

.05TW

1.5TW

10-0 . axial position (m) I I I I

9-

8-

- z ; 7- 3 -0 .- E! 6.4

radial expansion of electron

of the traveling wave causes the emitted electrons to return to the high voltage electrode, and power levels of 1 TW or greater can be transmitted. A two dimensional computer simu- lation of a magnetically insulated coaxial line demonstrates this ef- fect. At the head of the pulse, the electrons reach the ground elec- trode, but within a short distance into the pulse, they are turned back and the power is transmitted effi-

.

MITE

ciently. This principle has been dem- onstrated on our Magnetic Insula- tion Test Experiment (MITE), one module of the 36 module EBFA. A 7-meter (M), long, magnetically in- sulated line was tested at the 1 TW level showing - 90% efficiency of energy transport. We are using a tri-plate line inside a cylindrical vacuum chamber, rather than a coaxial line. This permits tighter packaging of the output beams

near the target. In addition, by tap- ering the MITL, the power density can be enhanced to greater than 10 W/cm2 before the beam is formed in each diode. The multiple beams would then be transported from the exit point of the vacuum line via a plasma channel to the target as previously described. Both relativistic electrons and non- relativistic light ions are being con- sidered for this approach to power concentration and beam transport.

ICF program power goals

Targets The-targets d-signed fa rticle beam applications are of necessity larger and thus more massive than laser targets because of the longer pulse durations of the source and more limited focusing capabilities of energetic particles. This means that our targets can reach higher levels

10'6

1 0i4

> c m S U

.- -

10'2

10'0 I I In temperature KeV 1 10 100

of confinement more easily with the greater levels of energy available, but must be optimized to reach high temperature. Here we see the familiar path being pursued in the ICF laser program in comparison with the electron and ion ap- proaches. We are closer to the re- quired values of n7 (ignition

condition) and our experiments are emphasizing way.s to achieve the necessary high temperatures. The data point representing the 1976 Kurchatov result was achieved using. a comparatively modest power level but employed a method for enhancement of the compressional heating of the fuel.

magnetic confinement fusion inertial confinement fusion inertial confinement fusion with magnetic thermal insulation

Magnetic field holds heat. Collapsing shell confines and heats fuel. Energy is lost to wall by electron thermal conduction.

Magnetic field reduces loss giving higher fuel temperature.

imploding target hologram

In other target work we are study- ing the dynamic behavior of implod- ing cylinders to determine the required symmetry of irradiation and material properties. We have observed (using holographic inter- ferometry) that exploding pusher targets implode in a stable manner even with large initial perturbations, but that ablatively driven targets have much more stringent sym- metry requirements. In other exper- iments we have seen evidence of particles of matter ejected from the inner surface of an imploding shell, and such studies are assisting us in defining the required beam un- iformity and target quality. The target approach which was first tested at Sandia in late 1976 with success, is to adapt an idea from magnetic fusion, i.e., use of a magnetic field to thermally insulate the fuel from the surrounding high density wall (electron conduction is inhibited). If the fuel is preheated with a high current discharge prior to implosion, the resulting embed- ded magnetic field allows higher final fuel temperatures. Using such a target, we have produced 106 deuteruim-deuterium (DD) neu- trons, and deuterium-tritium (DT) experiments are now underway. The DT neutron pulse from an im- ploded target using preheat and magnetic thermo-insulation has an easily characterized fast neutron pulse which arises at the time of target implosion. This clearly de- fined pulse shape can be easily distinguished from background

- . -.-. ~.

_ . . . . . .

D-T neutron signal

enhanced deposition I

f straight path-no field

increased path length and beam stagnation due to magnetic fields

multiple passes-electric and/or magnetic fields

neutrons which might be a source of spurious results. This type of target is continuing to be evaluated because of its promise in reducing the beam power needed for ignition. Another aspect ot our target related research involves the question of beam deposition in the outer layer of the target. In order to reduce the amount of mass needed to effec- tively stop the electrons and thus

:; .

the necessary beam energy, it is important to rely on beam self-field effects for range shortening. If self-electrostatic and magnetic ef- fects are ignored, a 1 MeV electron would deposit only 10% of its energy in a 10 p m thick gold foil. On the other hand, according to deposition calculations, the self- field of a 1 MA beam should re- duce the electron penetration

length and increase the absorption efficiency to 90%. In a simplified sense, this effect can be explained by-stagnation of the beam elec- trons thus giving each electron more opportunities to interact with the thin foil via classical collisions. Evidence for enhanced deposition has been observed in our lab as well as in labs in Japan, Israel and the Soviet Union.

calculated deposition for an 800 KeV 2 mm beam radius IO pm thick Au foil

lo4 beam current (amps) IO5 106

i

I

Ion Beam The other particle beam approach receiving increased emphasis in the U.S. is the use of light ion beams generated with the s a m e pulsed power technology as that used for electrons. Here the goal is to efficiently suppress the electron flow and to extract from the diode a

converging light ion beam. We, to- gether with a group at Cornell Uni- versity, are investigating use of electron suppressing magnetic fields applied by pulsed coils; a similar ion beam effort at the Naval Research Laboratory is emphasiz- ing the suppression of the electron flow by self-magnetic fields in the high current diodes. In one diode configuration being considered for

EBFA, multiple ion beams are geometrically focused over a dis- tance of less than 1 M and then transported in plasma discharge channels to the target. By increas- ing the voltage during the power pulse, the ion beam can be bunched longitudinally as it propa- gates to the target, thus increasing the power by more than a factor of 5.

hypothetical ion beam voltage and power

2

1

> I -

.6 -

.4 -

0 I 0 time (nsec) 50

calculated power of bunched ion beam

arrival time 175 180 185 (nsec)

proton beam from one 34 cm diameter ion diode channel length = 2.5m - maximum injection angle-16"

:::

The Electron Beam Fusion Ac- celerator (EBFA) is to be con- structed in a new facility which is to be ready for occupancy in the fall of 1978. The accelerator will initially consist of 36 modules delivering 1 MJ total, and is being constructed to permit a later upgrade to more than 2 MJ. The entire facility, which will not be completed until 1983 at the soonest, will also include a systems integration experiment whose ob- jective is to demonstrate the necessary repetitive pulse capabil- ity for future reactor related exper- iments, which could follow in the 1990's.

Many of the energy storage, switch- ing and pulse focusing elements of EBFA have been tested on our Proto I I accelerator, which has op- erated at the 8 TW level. Multiple electron beam and ion beam de- velopment experiments are planned for the near future on this machine.

Proto II

I

Electron Beam Fusion Facility-aerial view

Electron Beam Fusion Facility-interior view

I

Budget

since its inception in 1973; slower growth is expected through the net

Sandia's Particle Beam Program budget has grown substantially

energy gain experiments in 1985. The EBFA upgrade and systems in- tegration facility costs are esti- mated to be - $30M, and this expansion is being requested for first substantial funding in FY '81. This schedule will permit us to ob- tain sufficient experience with Proto 11, MITE and EBFA to define the upgrade components with minimal risks.

: I

I

I

i

*O 1 15

I construction - 10

5

MS

n 75 76 77 78 79 80 81 82 83

Issued by Sandia Laboratories, operated for the United States Department of Energy by Sandia Corporation.

NOTICE

This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Department of Energy, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that i t s use would not infringe privately owned rights.

Printed in the United States of America

5/78/1000

i

United States Department of Energy

D r